The present invention relates to load response control, and more particularly, to a method of implementing load response control wherein a time delay is inserted in the regulation loop of an electrical alternator for isolating the latter from transient electrical loads.
Most, if not all, of today's motor vehicles include a mechanically-driven DC generator electrically coupled to a battery. An alternator is one example of the DC generator which supplies the power to the electrical system and recharges the battery as required. The alternator includes rotating magnetic field windings magnetically coupled to stationary stator windings for providing output power as a function of the speed of the rotation and the current flowing in the field windings. The rotating field windings are coupled to the output of a voltage regulator via metallic brushes. The regulator monitors the variation in the system supply voltage and controls the current flowing in the field windings in response thereto, wherein the output power of the alternator is adjusted by increasing the field current as the supply voltage drops and decreasing the field current with increasing supply voltage.
Variation in the output power requirements of the alternator are transferred to the engine as a mechanical load. A sufficiently large electrical load forces the regulator to assert maximum field current in response to the corresponding drop in supply voltage. The alternator in turn transfers a large torque load to the engine causing a noticeable reduction in RPM (revolutions per minute) which may be annoying to the operator of the motor vehicle. If the engine is operating at idle speed, the reduction in RPM may even cause the engine to stall.
One technique to solve this problem is disclosed in U.S. Pat. No. 4,459,489 which monitors the system supply voltage and trips a comparator when the supply voltage drops below a predetermined threshold. The transition of the output signal of the comparator triggers a one-shot monostable multivibrator. A voltage is maintained across a first capacitor representative of the last known value of current flowing in the field windings of the generator. The pulse from the multivibrator causes the voltage across the first capacitor to be transferred to a second capacitor, which in turn biases an oscillator for providing a signal having a duty cycle proportional to the bias voltage. The duty cycle increases as the voltage across the second capacitor decays, thus, the output signal of the oscillator, which controls the field current in the generator, is pulse width modulated to slowly increase the field current as a function of the discharge rate of the second capacitor.
One problem with the '489 patent is that the regulation of the field current is not controlled in real time with dynamic variation in the system loading. Once the low voltage has been detected and the one shot triggers the transfer of the capacitor voltage, the regulator continues to ramp up the field current until the time constant of the second capacitor is completed regardless of subsequent changes in the load. Thus, the field current continues to increase even though the load may have in fact been removed during the time constant of the second capacitor.
Thus, what is needed is a method of implementing load response control which provides real time regulation of the alternator in response to dynamic loading conditions while at the same time isolating the alternator from the adverse effects associated therewith.